The present invention relates to a rotary valve assembly and a method of assembling a rotary valve. More particularly the invention concerns a rotary valve of the type having a sleeve member, a rotor member within the sleeve member and relative rotation between which members about an axis and from a neutral condition causes an adjustment in the valve, C-spring means circumferentially biasing the sleeve member relative to the rotor member and the assembly to said neutral condition, the C-spring means being located around the axis and having a mouth within which is located a first abutment secured relative to the rotor member and a second abutment secured relative to the sleeve member, the abutments reacting against the C-spring means in the mouth thereof to enlarge the mouth during relative rotation between the rotor and sleeve members to effect the said biasing--such a rotary valve will hereinafter be referred to as "of the type specified".
Rotary valves of the type specified are frequently employed in power assisted vehicle steering gears where relative rotation between the rotor and sleeve members in response to a steering input torque and from the neutral condition adjusts the valve to control the power assistance which is provided. The biasing of the C-spring means, either independently or in combination with other spring biasing such as a torsion rod as is well known in rotary valves, causes the rotary valve to revert to its neutral condition upon removal of the input torque; an example of a rotary valve of the type specified is to be found in the assignee's British Patent Specification No. 1,603,198.
For efficient operation of a rotary valve of the type specified it is desirable that the valve is correctly set-up (sometimes referred to as "balanced") when in its neutral condition, that is to say that the spring biasing means which reacts between the rotor and sleeve members should bias those members rotationally relative to each other and to the neutral condition in which condition fluid flow, if any, through the valve should present predetermined, balanced, characteristics. A typical rotary valve of the type specified for a power assisted vehicle steering gear will provide open centre, open return characteristics in its neutral condition and in this condition a supply of fluid under pressure to a common inlet port of the valve should provide pressure drops which are balanced over outlet ports of the valve these ports corresponding to connections on the valve, for example, to opposite sides of a power assistance ram and to a fluid exhaust or return. A rotary valve which does not provide balanced characteristics in a neutral condition as aforementioned is undesirable as it will be appreciated that, particularly in a power assisted steering gear, the use of such a valve can adversely affect the characteristics of the steering gear to an unacceptable extent.
It is an object of the present invention to provide a rotary valve of the type specified and a method of assembling such a valve by which the characteristics thereof in a neutral condition can be determined to alleviate the disadvantages discussed above.